The present invention relates to a method of controlling the output of a photosensor and, more particularly, to a photosensor installed in a copier or the like to sense a sheet and an output control method therefor.
A photosensor, comprising coactive light emitting and light receiving elements, finds various applications such as to a copier and serves to check presence/absence of a document, copy sheet or the like. While the light emitting element is a light emitting diode for emitting a specific quantity of light proportional to the magnitude of a current fed thereto, the light receiving element is a phototransistor for generating a signal whose level corresponds to the quantity of input light. The light emitting diode and phototransistor are arranged to face each other in a predetermined position for detection or wait position, so that a sheet, whether being a document or a copy sheet, may be passed therebetween. When a sheet is present in the wait position, it intercepts the light emanating from the light emitting diode causing the phototransistor to deliver a signal which is lower in level than a predetermined reference voltage. When a sheet is absent in the specific position, the light from the light emitting diode becomes directly incident on the phototransistor to cause the latter to output a signal higher than the reference voltage. The presence/absence of a sheet, therefore, is represented by the magnitude of the output signal of the phototransistor relative to the reference level.
A problem heretofore encountered with such a photosensor is that the quantity of light issuing from the diode or the quantity of light incident on the phototransistor tends to fluctuate due to misalignment of optical axes of the coactive two elements caused by an inaccurate relative position thereof, or due to scattering in the characteristics of light emitting diodes and phototransistors. For example, the photosensor might cause the output signal of the phototransistor to remain lower than the reference level despite the absence of a sheet in the predetermined wait position. An expedient heretofore proposed against this problem is a variable resistor or the like which varies the magnitude of a current fed to the light emitting diode. In the accidental situation concerned, the variable resistor is manually operable to increase the current supplied to the light emitting diode and thereby the quantity of light issuing therefrom, thereby raising the output level of the phototransistor beyond the reference level.
The manual adjustment, however, consumes disproportionate time and labor and is not always successful to accurately attain the optimum result.